[Ndn-interest] [EXT] content store

Junxiao Shi shijunxiao at email.arizona.edu
Mon Feb 22 19:32:58 PST 2021

Hi Marwa

> 1- In the content store you are using skip lists and hash tables in older
> versions 0.7.x, is the skip lists and hash tables have the ability to store
> the data packets?
> because in the repository the btrees have been used, why? I,m confused
> about this point.

Typically the Content Store has an *index* pointing to packet buffers.
When someone says the CS is a hash table, tree, trie, skip list, etc, it
refers to the structure of the index.

The packets themselves are stored in buffers elsewhere.
In NFD, buffers are allocated via malloc; in NDN-DPDK, buffers are fetched
from a pre-allocated mempool; I don't know how ccnd handles buffers.

2- why the number of contents have been used to measure the capacity of the
> content store and not something like (200MB, 300MB, ...)?

As I described above, a forwarder stores packets in buffers.
In both NFD and NDN-DPDK, a buffer is allocated before receiving the packet
from a socket or Ethernet adapter, and the packet stays in the same buffer
until it's evicted / deleted.
Since the packet length is unknown before receiving, every buffer must be
able to accommodate the maximum packet length (around 9KB).

As such, the CS capacity in bytes equals the CS capacity in packets
multiplied by the maximum packet length.
It has nothing to do with the actual packet length.
In this case, it's easier to measure CS capacity in packets.

Yours, Junxiao

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